An apparatus for mounting semiconductors of this type is known in the art as a “Die Bonder”. It serves to mount the numerous, uniform chips of a wafer that are located next to each other on a carrier, mostly a tape, one after the other onto a substrate, eg, a metallic leadframe. Co-ordinated with each Pick-and-Place movement of a chip gripper, a wafer table on which the chip carrier is located presents a next chip and the substrate is transported likewise in order to present a new substrate position at a second location. In order to pick and subsequently place the chip, the chip gripper can be raised and lowered either together with the entire Pick and Place system or independently in relation to the Pick and Place system.
Extremely high demands are placed on automatic assembly machines of this type. For the further processing of the mounted chips, they must be accurately positioned on the substrate which demands a correspondingly accurate reaching of the second location by the chip gripper and already demands the accurate reaching of the first location for picking the chip. On the other hand, high speed and short cycle times are required through which correspondingly high accelerations and forces of inertia occur at the moved parts.
Up to now, in order to produce the alternating movements of the chip gripper, various lever mechanisms have been applied some of which include crank guides. Because of the substantial lateral forces occurring at them, guides of this type are unfavourable for a precise movement process and have to be appropriately maintained. With another known mechanism, the chip gripper sits at the end of a lever that swivels back and forth, ie, it makes an arc-shaped movement corresponding to the swivel deflections of the lever each of which has to be stopped in the end positions whereby a strong tendency to oscillation exists. A disadvantage of such lever-operated mechanisms lies in that they only allow the transport of the chip along a fixed, predetermined path from a location A to a location B. Pick and Place systems with lever mechanisms are known for example from the patent documents EP 877,544, U.S. Pat. No. 6,185,815 and WO 97/32460.
Pick and Place systems are also known with which the chip gripper is driven by means of a toothed belt. The disadvantage here is the great inaccuracy in placing the chip onto the substrate.
On the one hand, in order to be able to mount the semiconductor chips quickly and accurately, the distance between the pick location and the mounting location should be short and, on the other hand, the mechanical construction should be simple. The Pick and Place system of EP 923,111 is indeed a simple and robust construction that enables a precise placing of the semiconductor chip onto the substrate but has the disadvantage that the space requirement continues to increase as the diameter of the wafers continues to increase. The equally known solution with which the substrate table and the wafer table are arranged one above the other has the disadvantage that, from the pick location to the mounting location, a large difference in height has to be overcome.
The Pick and Place system known from WO 97/32460 with which the wafer table is arranged orthogonally to the substrate table has the disadvantage that occasionally semiconductor chips that stick to the foil fall down and that the foil distorts as the result of the force of gravity acting upon the semiconductor chips so that the position of the semiconductor chip to be picked changes unintentionally. Furthermore, it can happen that now and then the foil inclines out of the vertical plane. In doing so, the corners or edges of neighbouring semiconductor chips that are only separated by small saw cuts could come into contact. In the worst case, such contacts can lead to corners or edges of the semiconductor chips breaking off which is known in the art as “Chipping”.